Mobile communication services have recently provided various services such as broadcasting, multimedia videos, e-mails, multimedia messages, and the like, to examine a possibility of opening a new market. The advent of the information era requests wireless multimedia services with a variety of qualities, for example, from a slow speed to a high speed and from a real time to a non-real time.
Accordingly, new research is conducted so that a mobile communication system can use techniques for effectively allocating a resource (i.e., a frequency channel), that is, a limited frequency band between users. In association with this research, a wireless communication system proposes wireless transmission techniques, for example, wireless multiple access and multiplexing, high-speed packet wireless transmission, wireless link control, and the like.
In particular, a Hybrid Automatic Repeat Request (HARQ) scheme related to a wireless link control scheme controls errors by combining Automatic Repeat Request (ARQ) and Forward Error Correction (FEC), thereby improving data transmission reliability. As a result, the HARQ scheme can apply to a packet data service of which a packet is generated in a burst manner similarly to a wireless Internet packet.
When using the HARQ scheme, a receiving end determines whether a response is either affirmative (hereinafter, acknowledgment (ACK)) or negative (hereinafter, Negative-ACK (NACK)) according to a result obtained by performing decoding on transmitted data, and transmits the determination result to a transmitting end so as to request the transmitting end to retransmit the same data. In this mechanism, if the receiving end determines a NACK response according to the decoding result, the transmitting end retransmits corresponding data. Accordingly, the receiving end combines retransmitted data with previous data, thereby improving reception capability. In this case, the receiving end determines whether data transmitted for an HARQ operation is newly transmitted data or retransmitted data, and stores the transmitted data to improve data combining capability. Therefore, for a proper HARQ operation, transmitted HARQ data needs to be controlled, and a memory for storing the HARQ data needs to be effectively controlled and managed.
The 802.16 standard and the Mobile WiMax standard are wireless standards related to the HARQ scheme. In these standards, a transmitting end allocates HARQ data and a receiving end transmits an ACK/NACK response (i.e., ACK_RSP) for the HARQ data according to an ARQ Channel Identifier (ACID). The ACID is identification information for identifying HARQ data. An ACK channel corresponds to a region allocated to transmit ACK/NACK information by the receiving end to the transmitting end as a result of error detection performed on the HARQ data. In addition, new transmission/retransmission for a downlink HARQ burst is determined according to indication information of an allocation message of the HARQ data. For example, new transmission/retransmission can be determined according to a toggle state (i.e., ‘0’ or ‘1’) of AI_SN field information of an ‘HARQ DL-MAP message’. That is, when allocating an HARQ burst for a corresponding ACID, if AI_SN information is identical to AI_SN information for current HARQ burst allocation, it implies retransmission, and otherwise, it implies new transmission.
When using the HARQ scheme, previous data and newly received retransmission data have to be combined with each other, and thus data storing is a necessary process. A data storage space has been increasing as a higher speed is demanded by communication systems. A memory size required to store HARQ data is determined according to the number of bits of Log Likelihood Ratio (LLR) information. The greater the number of bits of the LLR information stored in a memory, the higher the data combining capability and the decoding capability. However, a memory size increases to the extent of the increased number of bits. Therefore, an effective structure of a communication system depends on a combining method of an HARQ combiner and a determination result on the number of bits of the LLR information. Accordingly, there is a need for an HARQ combining method capable of effectively using and managing a limited-sized memory while improving capability when using an HARQ scheme.